Biological function and molecular mapping of M antigen in yeast phase of Histoplasma capsulatum.
Histoplasmosis, due to the intracellular fungus Histoplasma capsulatum, can be diagnosed by demonstrating the presence of antibodies specific to the immunodominant M antigen. However, the role of this protein in the pathogenesis of histoplasmosis has not been elucidated. We sought to structurally and immunologically characterize the protein, determine yeast cell surface expression, and confirm catalase activity. A 3D-rendering of the M antigen by homology modeling revealed that the structures and domains closely resemble characterized fungal catalases. We generated monoclonal antibodies (mAbs) to the protein and determined that the M antigen is present on the yeast cell surface and in cell wall/cell membrane preparations. Similarly, we found that the majority of catalase activity was in extracts containing fungal surface antigens and that the M antigen is not significantly secreted by live yeast cells. The mAbs also identified unique epitopes on the M antigen. The localization of the M antigen to the cell surface of H. capsulatum yeast and the characterization of the protein's major epitopes have important implications since it demonstrates that although the protein may participate in protecting the fungus against oxidative stress it is also accessible to host immune cells and antibody.
Guimarães
Allan Jefferson
AJ
Division of Infectious Diseases, Department of Medicine and Microbiology and Immunology, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York, USA.
Hamilton
Andrew John
AJ
de M Guedes
Herbert Leonel
HL
Nosanchuk
Joshua Daniel
JD
Zancopé-Oliveira
Rosely Maria
RM
D000595:Amino Acid Sequence; D000908:Antibodies, Fungal / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D000946:Antigens, Fungal / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D002374:Catalase / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D006658:Histoplasma / Q000276:immunology* / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018384:Oxidative Stress; D010802:Phylogeny; D016415:Sequence Alignment; D015003:Yeasts / Q000276:immunology
D000908:Antibodies, Fungal; D000911:Antibodies, Monoclonal; D000946:Antigens, Fungal; D000939:Epitopes; D006023:Glycoproteins; C118415:M antigen, Ajellomyces capsulatus; D002374:Catalase